In one known type of blind rivet, the head of the mandrel is shaped so as to be able to penetrate into the tubular bushing during tensioning in order to enlarge the same and to thus create a holding surface against the materials. French patent 2,306,361 or British patent 1,330,501 show, for example, rivets of this type. However, the bearing surface obtained by means of these rivets is very limited and, because of the enlarging, its direction is very inclined in the axial direction: such a bearing surface has a low vibration resistant and insecure holding, while it leads to a deleterious deformation of the materials at the edge of the hole. In particular, this deformation is unacceptable in the case of fragile materials (laminated,fiber reinforced synthetic materials) which are damaged at the edges of the hole with delamination and fraying of the fibers and of the binder.
In certain fastener members, the stem portion of the sleeve or bushing is divided into several sectors by means of longitudinal slots, and during tensioning of the mandrel, these sectors open and fold back on themselves to form several small gripping strips which come to rest against the materials to be assembled. For example, U.S. Pat. No. 4,289,061 shows such a member in which three longitudinal slots define three foldable sectors which are caused to open to form three material holding strips. However, the gripping or holding surface thus created is discontinuous and its holding ability is for this reasons considerably reduced, not only by reason of the reduction in its peripheral surface, but also and especially by reason of the discontinuity of the material around the periphery of the sleeve. Further, the materials to be assembled are held at the periphery of the hole by a series of holding zones separated by free zones, which is very undesirable, especially in the case of fragile materials where the stresses created at the junction of these zones may cause local damage. Further, the production of the securing members is more complex than in the preceding case by reason of the cutting of sectors which constitutes a delicate operation requiring high precision.